The invention relates to a joint endoprosthesis, in particular for knee prostheses, which by a first implant component can be attached to a first epiphysis and by a second implant component to a second epiphysis of two epiphyses that form a joint, wherein the first implant component and the second implant component each have articulation surfaces for the formation of a swivel joint enabling swiveling about a swivel axis directed roughly transversally with respect to the longitudinal extent of the first and second bones that have the first and second epiphyses, and which furthermore has a sliding piece which additionally enables a rotational movement and a translational movement of the epiphyses relative to each other, with the rotational movement being about an axis of rotation roughly transversal to the swivel axis and roughly in the longitudinal direction of the first bone and the translational movement being in a plane that is roughly parallel to the swivel axis and roughly transversal with respect to the axis of rotation.
The first generation of serviceable knee joints was fitted with a hinge-type joint. These axial knee joints, whose motion was constrained in cases with very poor axial conditions and extreme ligament instabilities, are in use even to date in limited number. In fact, constrained motion does remedy the instability but it causes substantial disadvantages such as increased stress on the material and above all loosening of the implants from their anchoring in the bone.
A next major generation of knee joints consists of so-called surface prostheses, which merely create new artificial sliding surfaces in cases where wear of cartilage and menisci must be compensated for while the natural system of ligaments and soft parts still maintains the stability of the joint.
The broad application of surface prostheses initially caused a substantial improvement of femoral-tibial joint articulation. This type of prostheses allows the largely preserved ligament system a considerable range of motion of the femural and tibial sliding surfaces. These are so-called "flat" forms, i.e. sliding surfaces that are configured as flat as possible. Yet, this development at the same time led to severe setbacks in the development of artificial knee prostheses. With all of these prosthesis designs the metal femoral skid in motion only has point-like or linear support on the polyethylene sliding surface of the tibia, an implant material which is indispensable to date. Excessive lump loading of the polyethylene sliding surface often leads to premature destruction of superficial sliding portions as well as of portions lying below the loaded, resulting in more or less markedly increased abrasion conditions which may lead to bone irritation, destruction of bone and dissolution of bone (osteolysis). As a whole, this abrasion phenomenon can be referred to as polyethylene disease, which may induce premature dysfunction of the artificial joint and the bone.
These histological, tribological and clinical recognitions introduced the development of a new generation of artificial knee sliding surfaces. What this development wants to achieve is the provision of new surface structures of the sliding partners and improvement of the anchoring conditions in order to arrest premature loosening of the implants, which arises due to increased abrasion and due to incorrect loading of the implants.
The natural conditions of movement of the knee joint are complex and cannot be imitated completely by artificial constructions. The dominant flexion and extension movements in a complex manner are connected with motions of rotation whose center of rotation shifts constantly, namely due to the one sliding partner being dislocated in anterior-posterior direction (AP) by the so-called rolling-sliding movement. This complex biomechanical motion is constantly influenced by additional factors such as conditions of the ligament system in lateral and in AP direction as well as of the articular capsule, muscular tension, patella tension and above all the axial changes of the bone geometry of the femur and tibia.
The efforts of the current generation of knee joints are moving away from the "flat" forms in favor of the more conformal types, since low conformality leads to excessive ,contact stress" of the polyethylene, which in turn causes increased abrasion. Increased conformality on the other hand carries in it the danger of limiting the motion. After all, the rotation and gliding movements in AP direction are not to differ too much from the natural conditions. Current efforts are directed toward achieving a high level of conformality without limiting the rotational and gliding movements. There already are functioning knee joints (U.S. Pat. No. 4,340,978 and U.S. Pat. No. 4,309,778), which on the one hand allow the rotational movement, so-called "rotating-platform" and on the other hand "artificial menisci", so-called "meniscal bearings", which travel in AP direction on a kind of guiding track mechanism and imitate AP dislocation. The knee joints known from the two above-cited US Letters Patent are complicated in construction in that between the first and the second implant component two sliding bodies are inserted on the first implant component which are arranged at a distance from each other and are guided in tracks on the first implant component and which constitute the articular surfaces for the formation of a swivel joint, which sliding bodies enable both a motion of rotation and a swiveling motion since the guiding tracks are arranged in the shape of an arc. One disadvantage of this is, however, that the guiding tracks lie completely exposed and open toward the joint and that the rotary motions can only be carried out precisely in accordance with the guiding tracks, as a result of which translational motion is no longer possible. However, in accordance with another embodiment according to these US Letters Patent the guiding tracks have very much clearance, thus allowing not only rotational movements but also, to a very limited extent, translational movements, but as a result thereof the rotational movements are entirely uncontrollable and are not orientated according to an axis of rotation. To date, it has not been possible to find a satisfactory way of combining the two motions, namely the rotational movement and the translational movement, since the rotating platform does not travel and the track-guided meniscal motion is not or hardly capable of rotation. In particular, it is not possible to date to carry out translational movements independently of the rotational movement, i.e. in any rotational position.